Softening of water by thermal action is a well-established principle and commercial equipment for accomplishing this purpose is available through a number of companies, such as Graver Water Conditioning Company of Union, N.J. Generally, this type of equipment requires a large volume of steam, i.e., great amounts of heat energy to effect the softening of large volumes of water; thus, such equipment is typically used where waste steam is available. Flash distillation of water is also old in the art for the purification of the water itself. Impure water is heated by steam in a prime or brine heater and is introduced into a series of flash chambers at successively lower pressures, thereby flashing to corresponding lower temperatures. The water vapor, generated by the flashing in each chamber, is condensed on the outer surface of metal tubing through which the impure water is passed. The heat given up by the condensing vapor serves to heat the impure water by flowing countercurrent to the direction of flow of the flashing liquid. The impure water is thus heated almost to the desired purifying temperature and additional heat necessary to initiate flashing is provided in the prime or brine heater.
This particular process privides a stream of purified distillate which is caught in trays located beneath the tubular condensers and conducted by suitable pipes to the outside. However, preheating of impure water as it flows through metal tubing toward the heater causes scale to form on the inner surface of the tubing, thereby inhibiting proper waterflow therethrough.
In U.S. Pat. No. 3,329,583, issued to D. F. Othmer, a water purification technique is disclosed. In this patent, the flashing of water is used in two different ways. In the first way, the water is flashed to heat hard or impure water flowing through tubing on its way to a prime or brine heater. In the second way, flashed water vapor is urged into direct contact with relatively pure water, not to heat the latter but to recover water vapor caused by the water flashing to thereby increase the volume of the pure water itself. This pure feed water is then collected and used or stored.